The majority of projects in this program project grant will rely heavily on transgenic mice, some of which have already been generated and others of which need to be generated. During the past five years, existence of this core has greatly facilitated the ability of the laboratories directed by Rob Edwards, David Copenhagen, Louis Reichardt and Michael Stryker to exploit this powerful technology. During the next five years, we anticipate expanded use of this core that will almost certainly be used by all members of our new program project team. The existence of a core has made it possible to hire a senior specialist with more than 15 years of relevant experience in preparing transgenic mice plus a junior technician able to manage the mouse colonies and perform routine genotyping, etc. The former person has helped our laboratories generate more than a dozen transgenic lines and half a dozen knockout strains. The more junior technician has been particularly valuable in helping the labs entering this field. All laboratories will continue to benefit from a transgenic core with a person dedicated to performing well certain tasks of critical importance in generating such animals. To help culture and screen ES cells, provide transgenic animals with targeted mutations and provide help in training postdoctoral fellows and graduate students in this important technology, we propose to maintain a modestly-sized and staffed core facility with a cell culture facility for embryonic stem cells, equipment for injection of single cell embryos and blastocysts, and a mouse colony with fertile and vasectomized males and fertile females for use as single cell embryo or blastocyst donors and pseudopregnant recipients. The Reichardt laboratory will provide the supervision and expertise for setting up and managing this facility under the overall guidance of the Principal Investigator.